Bicycle hub transmission

ABSTRACT

A bicycle hub transmission includes a hub axle, a driver, a hub shell, a power transmission mechanism and a shift mechanism. The driver and the hub shell are rotatably supported relative to the hub axle. The power transmission mechanism is disposed between the driver and the hub shell to selectively transmit rotational power from the driver to the hub shell through one a plurality of power transmission paths. The shift mechanism operatively couples the power transmission mechanism to select a power transmission path. The downstream planetary gear unit includes a planetary gear carrier that meshes with planetary gears of the upstream planetary gear unit or with a linking member coupled to the planetary gears of the upstream planetary gear unit. The planetary gear carrier of the downstream planetary gear unit is coupled with a brake unit to transmit a reverse rotational power from the driver to the brake unit.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119 to European PatentApplication No. 07012817.8, filed Jun. 29, 2007. The entire disclosureof European Patent Application No. 07012817.8 is hereby incorporatedherein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention generally relates to a hub transmission for a bicycle.More specifically, the present invention relates to an internally gearedbicycle hub transmission.

2. Background Information

Bicycling is becoming an increasingly more popular form of recreation aswell as a means of transportation. Moreover, bicycling has become a verypopular competitive sport for both amateurs and professionals. Whetherthe bicycle is used for recreation, transportation or competition, thebicycle industry is constantly improving the various components of thebicycle. One component that has been extensively redesigned is thebicycle drive train.

Internally mounted multi-speed hub transmissions are mounted to the rearwheel of a bicycle and allow a rider of the bicycle to select differentgear ratios to change the pedaling force. Typically a hub transmissionhas a hub axle that is mounted to the bicycle frame. The hub axlerotatably supports a driver for transmitting a pedaling force to the hubtransmission through a sprocket and a chain. The hub transmissionfurther comprises a hub shell which is likewise rotatably supported bythe hub axle.

The hub shell accommodates a power transmission mechanism which isdisposed between the driver and the hub shell for transmittingrotational power from the driver to the hub shell. The powertransmission mechanism provides a plurality of power transmission pathswith different gear ratios that can be selected by using a shiftmechanism, wherein each power transmission path typically produces aspecific gear ratio. To establish the plurality of power transmissionpaths the power transmission mechanism ordinarily has several planetarygear mechanisms.

Current internal hub transmissions are designed to provide 10 or morespeed stages. For example, one proposed internal hub transmission isdisclosed in German Patent Publication No. DE 10 2004 011 052 A1. Thehub transmission according to German Patent Publication No. DE 10 2004011 052 A1 allows a selection between 9 speed stages which are providedby a plurality of planetary gear mechanisms. The known hub transmissionhas three planetary gear mechanisms that allow the combination of threespeed stages with another five speed stages, for a total of nine speedstages with a gear ratio of 340%. The hub transmission includes a firstplanetary gear mechanism having a first sun gear that is non-rotatablymounted to the hub axle, a first planetary gear rotatably supported by afirst planetary gear carrier and a first ring gear. The first planetarygears are disposed between the first sun gear and the first ring gearand mesh with the same.

A second planetary gear mechanism includes a second sun gear which isarranged on the first planetary gear carrier. Second planetary gears aremounted on the first ring gear. A third planetary gear mechanism isformed similar to the second planetary gear mechanism, and includes athird sun gear mounted on the first planetary gear carrier. The thirdsun gear meshes with third planetary gears with each being non-rotatablyjoined to the respective second planetary gears. Thereby a two-stepplanetary gear is formed. The third planetary gears mesh with a secondring gear to transmit the torque of the third planetary gear mechanismto the second planetary gear mechanism.

The shifting mechanism of this hub transmission comprises a pawl carrierwhich allows coupling the driver selectively with components of therespective planetary gear mechanisms to produce different gear ratios.To this end the pawl carrier comprises a plurality of controllablepawls, namely six pawls that are actuated by means of three shiftingcams.

The arrangement of the two-step planetary gear on the first ring gear incombination with the second ring gear that meshes with the two-stepplanetary gears, leads to a pile type of internal hub transmission.Since the second ring gear overlaps the other components of the threeplanetary gear mechanisms, the diameter of the second ring gear and,thus, the diameter of the internal hub transmission is increased.Moreover, the pile type construction of the internal hub transmissionleads to an increased total weight of the hub.

As described above, the second and third sun gears are each mounted onthe first planetary gear carrier. Therefore, the second and third sungears each rotate together with the first planetary gear carrier aroundthe hub axle. In particular, the power transmission path for speedstages 8 and 9 comprises the driver, the sixth pawl and the firstplanetary gear carrier wherein the first planetary gears rotate aroundthe first sun gear. The power transmission path further has the firstring gear, the second ring gear, the first pawl, the pawl connecting thepower transmission with the hub shell and the hub shell. In speed stage8, the third planetary gear rotates around the third sun gear and inspeed stage 9 the second planetary gear rotates around the second sungear.

Due to this differential rotational type of the planetary gear mechanismthe power transmission paths are complicated. In particular the powertransmission paths for speed stages 8 and 9 inefficiently transmitpower.

A similar hub transmission is known from German Patent Publication No.DE 197 20 796 A1, which discloses a multiple speed hub having aplurality of planetary gear mechanisms arranged in series. The hubtransmission disclosed therein enables either a 7 speed shifting or a 14speed shifting. The 14 speed hub transmission comprises five planetarygear mechanisms, the components of which can be selectively locked toestablish the desired power transmission paths. A first planetary gearmechanism comprises a first sun gear rotatably supported by a hub axlewhich can be locked with the same. The first sun gear meshes with thesmaller diameter of a two-step planetary gear which is rotatablysupported by a first planetary gear carrier. The first planetary gearcarrier is non-rotatably connected with the hub shell. The largediameter of the two-step planetary gear meshes with a ring gear that canbe locked either with the hub axle or the first sun gear. A secondplanetary gear mechanism comprises a second sun gear rotatably supportedby and lockable with the hub axle. Second planetary gears mesh with thesun gear and a second ring gear wherein the second ring gear isnon-rotatably connected with the first sun gear. A third planetary gearmechanism comprises a third sun gear which is rotatably supported by andlockable with the hub axle. Third planetary gears mesh with the thirdsun gears which are non-rotatably connected with the second planetarygears with the respective second planetary gears. The second sun gearmeshes with the small diameter stage of the stepped planetary gears, andthe third sun gear meshes with the large diameter stage of the steppedplanetary gears.

The fourth and fifth planetary gear mechanisms are similar to the secondand third planetary gear mechanisms and are symmetrically formed andarranged. The fourth and fifth planetary gear mechanisms thereforelikewise comprise two-stage planetary gears, wherein the planetary gearsof the second and third planetary gear mechanism and the planetary gearsof the fourth and fifth planetary gear mechanisms are rotatablysupported by means of a common planetary gear carrier. The smalldiameter stage of the stepped planetary gears of the fourth and fifthplanetary gear mechanisms mesh with a ring gear that is non-rotatablyconnected with a driver.

A further embodiment of the 14-speed hub transmission is based on amodified embodiment of the above described hub transmission, and has asecond ring gear which meshes with both small diameter stages of thesymmetrically arranged stepped planetary gears. The common planetarygear carrier is replaced with two separate planetary gear carriers withthe planetary gear carrier of the second and third planetary gearmechanisms being non-rotatably connected with the first sun gear. Theplanetary gear carrier of the fourth and fifth planetary gear mechanismsis non-rotatably connected with the driver.

Owing to the increased number of clutches required for locking theseparate components of the planetary gear mechanisms, for example thering gears with the sun gears, the hub transmission according to GermanPatent Publication No. DE 197 20 796 A1 is complicated and comparativelyexpensive.

In view of the above, it will be apparent to those skilled in the artfrom this disclosure that there exists a need for an improved bicyclehub transmission. This invention addresses this need in the art as wellas other needs, which will become apparent to those skilled in the artfrom this disclosure.

SUMMARY OF THE INVENTION

One object of the invention to provide a hub transmission for a bicyclecomprising a plurality of speed stages and enabling a lightweight andcompact construction.

The foregoing objects can basically be attained by providing a bicyclehub transmission that basically comprises a hub axle, a driver, a hubshell, a planetary gear mechanism and a clutch. The driver is rotatablysupported relative to the hub axle. The hub shell is rotatably supportedrelative to the driver. The power transmission mechanism includes adownstream planetary gear unit and an upstream planetary gear unitdisposed between the driver and the hub shell to selectively transmitrotational power from the driver to the hub shell through one aplurality of power transmission paths. The shift mechanism isoperatively coupled to the power transmission mechanism to select one ofthe power transmission paths. The downstream planetary gear unitincludes a planetary gear carrier that meshes with planetary gears ofthe upstream planetary gear unit or with a linking member, which iscoupled to the planetary gears of the upstream planetary gear unit. Theplanetary gear carrier of the downstream planetary gear unit is coupledwith a brake unit to transmit a reverse rotational power from the driverto the brake unit.

A hub transmission structure with an integrated brake unit is known, forexample, from EP 06 008 957 which is assigned to Shimano, Inc. However,the known hub transmissions lack the specific coupling of the downstreamplanetary gear carrier with the upstream planetary gear carrier or withthe linking member wherein the brake unit is coupled with the downstreamplanetary gear carrier.

A hub transmission formed in accordance with the invention has a numberof advantages. Since the planetary gear carrier of the downstreamplanetary gear unit meshes with planetary gears of the upstreamplanetary gear unit a compact design is achieved that allows for aplurality of power transmission paths while maintaining a small diameterof the hub. The aforementioned coupling of the downstream planetary gearcarrier with upstream planetary gears further allows realizing theplurality of power transmission paths by means of a comparatively simplestructure that reduces the risk of a failure of components of thetransmission. Due to the surprisingly simple structure of the inventivehub transmission it is possible to produce a hub transmission thatenables a comparatively great number of gear ratios at relatively lowcosts. The invention has the further advantage that the planetary gearcarrier of the downstream planetary gear unit can be coupled with abrake unit to provide a hub transmission with an integrated brake.

In a preferred embodiment, the bicycle hub transmission has thedownstream planetary gear unit and the upstream planetary gear unitarranged to form at least four planetary gear mechanisms arranged inseries. Thereby it is possible to realize an 11-speed hub transmissionwith a compact design and a relatively small hub diameter.

Preferably, the downstream planetary gear unit constitutes at least afirst planetary gear mechanism and the upstream planetary gear unitconstitutes at least second, third and fourth planetary gear mechanisms

The first planetary gear mechanism preferably includes the planetarygear carrier of the downstream planetary gear unit and the third gearmechanism includes the planetary gears of the upstream planetary gearunit. This means that the first and third planetary gear mechanisms arecoupled by means of the downstream or first planetary gear mechanismwhich meshes with the upstream or third planetary gears.

Preferably, the planetary gear carrier of the downstream planetary gearunit includes a carrier portion and a ring gear portion which mesheswith the planetary gears of the upstream planetary gear unit or with thelinking member which is coupled with the planetary gears of the upstreamplanetary gear mechanism, with the carrier portion and the ring gearportion being non-rotatably connected as a unit. Hence, it is to beemphasised that the planetary gear carrier of the downstream planetarygear unit fulfils two functions, namely a support function for theplanetary gears of the first planetary gear mechanism and a powertransmission function for the planetary gears of the upstream planetarygear unit. Due to the non-rotatable connection between the carrierportion and the ring gear portion the compact design of the hubtransmission is optimized.

Moreover, it is possible to directly mesh the ring gear portion with theplanetary gears of the upstream planetary gear unit or alternatively toprovide, a linking member as an intermediate component between theupstream planetary gear unit and the ring gear portion, which is coupledwith the planetary gears of the upstream planetary gear mechanism.Thereby, it is possible to use different braking clutch means with theaforementioned embodiments.

Preferably, the planetary gear carrier of the downstream planetary gearunit is selectively connectable with the fourth planetary gearmechanism. Thereby, a number of further power transmission paths can berealized.

The connection of the planetary gear carrier and the downstreamplanetary gear unit with the fourth planetary gear mechanism can berealized, for example, by means of a preferred embodiment wherein theplanetary gear carrier of the downstream planetary gear unit includes aclutch engaging portion which is selectively connectable with aplanetary gear carrier of the fourth planetary gear mechanism.

To enable a transmission of a rotational force from the planetary gearcarrier of the downstream planetary gear unit to the hub shell, theplanetary gear carrier of the downstream planetary gear unit isselectively connectable with the hub shell by a first clutch to transmita rotational force from the planetary gear carrier to the hub shell.

In a preferred embodiment, the first planetary gear mechanism includesthe first sun gear, a first ring gear and a plurality of first planetarygears, with the first sun gear being rotatably supported by the hub axleand selectively lockable with the hub axle, the first ring gear beingcoaxially arranged with the first sun gear, and the first planetarygears meshing with the first sun gear and the first ring gear, the firstplanetary gears being rotatably supported by the planetary gear carrierof the first planetary gear mechanism. The first planetary gearmechanism corresponds to the downstream planetary gear unit.

Preferably, the first ring gear is selectively connectable with the hubshell by a second clutch for transmitting a rotational force from thefirst ring gear to the hub shell.

Preferably, the second planetary gear mechanism includes a second sungear, a second planetary gear carrier and a plurality of secondplanetary gears, with the second sun gear being rotatably supported bythe hub axle and selectively lockable with the hub axle, the secondplanetary gear carrier being rotatably supported by the second planetarygear carrier and meshing with the second sun gear.

Preferably, the third planetary gear mechanism includes a third sun gearrotatably supported by the hub axle and selectively lockable with thehub axle, with the planetary gears being rotatably supported by thesecond planetary gear carrier and meshed with the third sun gear.

Preferably, the planetary gear carrier of the third planetary gearmechanism and the second planetary gears of the second planetary gearmechanism are non-rotatably connected as a unit to form steppedplanetary gears respectively.

In a further preferred embodiment, the fourth planetary gear mechanismincludes a fourth sun gear, a second ring gear and a plurality of fourthplanetary gears, with the fourth sun gear being non-rotatably fixed tothe hub axle, the second ring gear being coaxially arranged with thefourth sun gear, and the fourth planetary gears being rotatablysupported by a third planetary gear carrier and meshing with the fourthsun gear and the second ring gear.

Preferably, the third planetary gear carrier engages with the secondplanetary gear carrier.

Preferably, a third clutch is disposed between the third planetary gearcarrier and the first planetary gear carrier, with clutch engagingportion arranged to selectively transmit a rotational force from thethird planetary gear carrier to the first planetary gear carrier. Afourth clutch can be disposed between the driver and the second ringgear to selectively transmit a rotational force from the driver to thesecond ring gear. A fifth clutch may be disposed between the driver andthe third planetary gear carrier to selectively transmit a rotationalforce from the driver to the third planetary gear carrier.

In a further preferred embodiment, the brake unit includes a cup whichis non-rotatably connected with the hub shell and forms acircumferentially disposed braking surface. The brake unit furtherincludes a plurality of brake elements arranged to co-operate with thebraking surface to apply a braking torque, and a plurality of controlelements to actuate the brake elements. The control elements are coupledwith the planetary gear carrier of the downstream planetary gear unitsuch that an actuation of the brake elements is effected by a reverserotation of the planetary gear carrier of the downstream planetary gearunit. This embodiment provides a reliable and compact brake unit whichis coupled with the planetary gear carrier of the downstream planetarygear unit to actuate the brake unit. As the planetary gear carrier ofthe downstream planetary gear unit operatively connects the brake unitwith the upstream planetary gear mechanism an optimal transmission ofthe reverse rotational force from the driver to the brake unit isaccomplished.

The first clutch can be disposed between the cup and the planetary gearcarrier of the downstream planetary gear unit. Thereby it is possible totransmit a forward rotational force from the planetary gear carrier ofthe downstream planetary gear to the hub shell via the cup which isnon-rotatably connected with the hub shell. This arrangement allows toreduce the length of the hub transmission and improves the compactdesign thereof.

The first clutch can be supported by a retaining element for the controlelements. This embodiment further minimizes the space used for the brakeunit.

In a further embodiment, the control elements comprise a plurality ofrollers which cooperate with a plurality of cam surfaces provided on theplanetary gear carrier on the downstream planetary gear. The retainingelement comprises a roller cage supporting the rollers wherein theroller cage is engaged with the planetary gear carrier of the downstreamplanetary gear unit. The engagement of the roller cage with theplanetary gear carrier of the downstream planetary gear unit enables asimple and efficient actuation of the brake units if the planetary gearcarrier is rotated in a reverse direction and, thus, also the rollercage. Thereby, the rollers contained in the roller cage cooperate withthe cam surfaces such that the rollers push the brake elements againstthe braking surface for applying a braking torque.

Preferably, the fourth clutch can be disposed between the driver and thesecond ring gear and includes a plurality of driving pawls and aplurality of braking pawls which are adapted to be selectively activatedby a forward or reverse rotation of the driver to rotate the second ringgear in a forward or reverse direction.

These and other objects, features, aspects and advantages of the presentinvention will become apparent to those skilled in the art from thefollowing detailed description, which, taken in conjunction with theannexed drawings, discloses a preferred embodiment of the presentinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the attached drawings which form a part of thisoriginal disclosure:

FIG. 1 is a longitudinal cross-sectional view of a hub transmissionaccording to an illustrated embodiment;

FIG. 2 is a longitudinal cross-sectional view of the hub transmissionaccording to FIG. 1 in speed stage 1;

FIG. 3 is a longitudinal cross-sectional view of the hub transmissionaccording to FIG. 1 in speed stage 2;

FIG. 4 is a longitudinal cross-sectional view of the hub transmissionaccording to FIG. 1 in speed stage 3;

FIG. 5 is a longitudinal cross-sectional view of the hub transmissionaccording to FIG. 1 in speed stage 4;

FIG. 6 is a longitudinal cross-sectional view of the hub transmissionaccording to FIG. 1 in speed stage 5;

FIG. 7 is a longitudinal cross-sectional view of the hub transmissionaccording to FIG. 1 in speed stage 6;

FIG. 8 is a longitudinal cross-sectional view of the hub transmissionaccording to FIG. 1 in speed stage 7;

FIG. 9 is a longitudinal cross-sectional view of the hub transmissionaccording to FIG. 1 in speed stage 8;

FIG. 10 is a longitudinal cross-sectional view of the hub transmissionaccording to FIG. 1 in speed stage 9;

FIG. 11 is a longitudinal cross-sectional view of the hub transmissionaccording to FIG. 1 in speed stage 10;

FIG. 12 is a longitudinal cross-sectional view of the hub transmissionaccording to FIG. 1 in speed stage 11;

FIG. 13 is a longitudinal cross sectional view of a hub transmissionaccording to an embodiment of the invention with a brake unit;

FIG. 14 is a longitudinal cross sectional view of a hub transmissionaccording to a further embodiment;

FIG. 15 is a cross sectional view of the brake unit along the line 15-15in FIG. 13;

FIG. 16 is a view of the hub transmission according to FIG. 13 with thebraking torque path through the hub transmission being illustrated; and

FIG. 17 is a view of the hub transmission according to FIG. 14 with thebraking torque path through the hub transmission being illustrated.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Selected embodiments of the present invention will now be explained withreference to the drawings. It will be apparent to those skilled in theart from this disclosure that the following descriptions of theembodiments of the present invention are provided for illustration onlyand not for the purpose of limiting the invention as defined by theappended claims and their equivalents.

Referring initially to FIG. 1, an 11-speed bicycle hub transmission isillustrated in accordance with one preferred embodiment. The hubtransmission is configured and arranged be mounted to the rear wheel ofa bicycle. The hub transmission basically includes a hub axle 1 and adriver 2 which is rotatably supported by the hub axle 1. The hubtransmission further includes a hub shell 3 which is rotatably supportedby the hub axle 1. A power transmission mechanism 4 is disposed betweenthe driver 2 and the hub shell 3 to selectively transmit rotationalpower from the driver 2 to the hub shell 3 through one of a plurality ofpower transmission paths that can be selected to change the gear ratioas desired by the rider.

To select one of the power transmission paths a shift mechanism 5 isprovided. The shift mechanism 5 corresponds to the shift mechanismdescribed in detail in European Patent No. EP 1 323 627 A2 and U.S. Pat.No. 6,607,465 B1 mentioned therein. The hub transmission has a pluralityof planetary gear mechanisms 6, 7, 8 and 9. The planetary gearmechanisms 6, 7, 8 and 9 are arranged in series and form at least fourplanetary gear mechanisms in the illustrated embodiment. The higher thenumber of the planetary gear mechanism 6, 7, 8 or 9, the closer it isarranged to the driver 2. For example, the second planetary gearmechanism 7 is closer to the driver 2 than the first planetary gearmechanism 6.

As mentioned above, the power transmission mechanism 4 has the planetarygear mechanisms 6, 7, 8 and 9 including a downstream planetary gear unitand an upstream planetary gear unit with the upstream planetary gearunit being arranged closer to the driver 2 than the downstream planetarygear unit. As seen in the direction of the rotational power flow, thedownstream planetary gear unit is arranged after the upstream planetarygear unit. For example, the downstream planetary gear unit includes thefirst planetary gear mechanism 6 and the upstream planetary gear unitincludes the third planetary gear mechanisms 8.

As is evident from FIG. 1, the downstream planetary gear unit has aplanetary gear carrier 31, and the upstream planetary gear unit hasplanetary gears 43 with the planetary gear carrier 31 of the downstreamor first planetary gear mechanism 6 meshing with planetary gears 43 ofthe upstream or third planetary gear mechanism 8.

In general, the planetary gear carrier 31 has a longitudinally extendingshape that is adapted to overlap components of the power transmissionmechanism 4 that are arranged upstream of the first planetary gearmechanism 6 and, thus, more proximate to the driver 2 than thedownstream planetary gear mechanism 6.

In particular, the planetary gear carrier 31 of the downstream planetarygear mechanism 6 axially extends from the area of the downstream orfirst planetary gear mechanism 6 to the area of the upstream or thirdplanetary gear mechanism 8. As illustrated in FIG. 1, the planetary gearcarrier 31 axially extends over more than ⅓ to ½ of the entire length ofthe hub transmission. The axial extension of the planetary gear carrier31 is such that the second planetary gear mechanism 7 which is arrangedbetween the downstream planetary gear mechanism 6 and the upstreamplanetary gear mechanism 8 is overlapped by the planetary gear carrier31. In the embodiment according to FIG. 1, the second planetary gearmechanism 7 is not engaged with the planetary gear carrier 31.

The planetary gear carrier 31 has a stepped shape with the innerdiameter of the subsequent steps increases towards the driver 2. Thestepped shape of the planetary gear carrier 31 will be described in moredetail in conjunction with the respective components associated thereto.

The planetary gear carrier 31 further comprises a (first) clutchengaging portion 31 c which is arranged on the axial end of theplanetary gear carrier 31 proximate to the driver 2. The clutch engagingportion 31 c is provided to engage with/disengage from a clutch 53(third clutch) which will be described in more detail in connection withthe fourth planetary gear mechanism 9.

The planetary gear carrier 31 further has a ring gear portion 31 b. Thering gear portion 31 b is integrally connected with a clutch engagingportion 31 c and is formed with a smaller inner diameter than clutchengaging portion 31 c. The ring gear portion 31 b meshes with planetarygears 43 of the upstream or third planetary gear mechanism 8. The innerdiameter of the ring gear portion 31 b is larger than the outer diameterof second planetary gears 42 of the second planetary gear mechanism 7 toavoid engagement or collision therewith.

The ring gear portion 31 b is integrally connected with a carrierportion 31 a which supports first planetary gears 41 of the firstdownstream planetary gear unit 6. The first planetary gears 41 arerotatably supported by first planetary gear shafts 41 a which aredisposed in the carrier portion 31 a of the planetary gear carrier 31.Typically, three ore more first planetary gears 41 are provided in thefirst planetary gear mechanism 6.

A further (or second) clutch engaging portion 31 d is integrally formedwith the carrier portion 31 a and is provided for engagingwith/disengaging from a first clutch 51 to establish/interrupt a powertransmission from the planetary gear carrier 31 to the hub shell 3. Thefurther or second clutch engaging portion 31 d is arranged downstream ofthe planetary gear mechanism 6. The ring gear portion 31 b and the(first) clutch engaging portion 31 c are located upstream of theplanetary gear mechanism 6. Again, the downstream or upstreamarrangement of components is seen and to be understood in the directionof the power flow.

The plurality of planetary gear mechanisms 6, 7, 8 and 9 will bedescribed in the following.

The first planetary gear mechanism 6 is arranged most downstream or mostdistant from the driver 2 with the first sun gear 11 being rotatablysupported by the hub axle 1 and selectively lockable with the hub axle1. Between an inner peripheral surface of the first sun gear 11 and thehub axle 1, a first sun gear guide ring 61 is non-rotatably fixed to thehub axle 1. The first sun gear guide ring 61 allows for the locking andunlocking the first sun gear 11 by means of the shifting mechanism 5.Coaxially arranged in relation to and rotatably supported by the hubaxle 1 is a first ring gear 21 with the first planetary gears 41 beingrotatably supported by the (first) planetary gear carrier 31 and meshwith the first sun gear 11 and the first ring gear 21.

As illustrated in FIG. 1, the first planetary gears 41 comprise two gearstages wherein the large diameter gear stage meshes with the first sungear 11 and the small diameter gear stage meshes with the ring gear 21.Small diameter gear stage of first planetary gears 41 is arrangedproximate to the second planetary gear mechanism 7. The ring gear 21 canbe connected with or disconnected from the hub shell 3 by means of asecond (one-way) clutch 52 which is disposed between the first ring gear21 and the hub shell 3.

As described above, the ring gear carrier 31 of the first planetary gearmechanism 6 extends axially beyond the planetary gears 41 in alongitudinal direction of the hub transmission thereby overlapping atleast the subsequently arranged upstream second and third planetary gearmechanisms 7, 8. The outer contour of first planetary gear carrier 31 isadapted to partially accommodate the ring gear 21 and forms a shoulder31 e such that the ring gear 21 is arranged between the shoulder 31 eand the large diameter gear stage of the first planetary gears 41.

The second planetary gear mechanism 7 is located upstream of the firstplanetary gear mechanism 6 and comprises a second sun gear 12 which isrotatably supported by and lockable with the hub axle 1. Between aninner surface of the second sun gear 12 and the hub axle 1, a second sungear guide ring 62 is non-rotatably fixed to the hub axle 1. A pluralityof second planetary gears 42 is rotatably supported by a secondplanetary gear carrier 32 which is rotatably supported by the hub axle1. To this end, the second planetary gears 42 are rotatably supported bya second planetary gear shaft 42 a which is supported by a secondplanetary gear carrier 32. Typically three or more second planetarygears 42 are provided.

The third planetary gear mechanism 8 is arranged upstream of the secondplanetary gear mechanism 7 and comprises a third sun gear 13 which isrotatably supported by and lockable with the hub axle 1. Between aninner peripheral surface of a third sun gear 13 and the hub axle 1, athird sun gear guide ring 63 is arranged and non-rotatably fixed to hubaxle 1. The third sun gear guide ring 63 can be actuated by means of theshifting mechanism 5 to lock/unlock the sun gear 13. A plurality ofthird planetary gears 43 meshes with the third sun gear 13 and isrotatably supported by the second planetary gear carrier 32. Inparticular, third planetary gears 43 are arranged on second a planetarygear shaft 42 a which, thus, represents a common planetary gear shaftfor the second and third planetary gears 42 and 43.

As is evident from FIG. 1, second and third planetary gears arenon-rotatably connected and integrally form a stepped planetary gear402. The small diameter gear stage of the stepped planetary gear 402meshes with the second sun gear 12, and the large diameter gear stage ofthe stepped planetary gear 402 meshes with the third sun gear 8.Moreover, the large diameter gear stage of the stepped planetary gear402 meshes with the ring gear portion 31 b of the downstream planetarygear carrier 31. Thus, it is possible to establish a transmission pathconnecting the third sun gear 8 with the first planetary gear carrier31.

A fourth planetary gear mechanism 9 is arranged upstream of the thirdplanetary gear mechanism 8 and represents the planetary gear mechanismclosest to the driver 2. The fourth planetary gear mechanism 9 comprisesa fourth sun gear 14 which is non-rotatably fixed to the hub axle 1. Asecond ring gear 22 is coaxially arranged with and rotatably supportedby the hub axle 1. Between the second ring gear 22 and the fourth sungear 14 a plurality of fourth planetary gears 44 is arranged which areformed as two-step planetary gears. The large diameter gear stage of theplanetary gears 44 meshes with the ring gear 22 and the small diametergear stage of the fourth planetary gears 44 meshes with the fourth sungear 14. Typically three or more fourth planetary gears 44 are provided.

The fourth planetary gears 44 are rotatably supported by a thirdplanetary gear carrier 33 which can rotate around the hub axle 1. Thethird planetary gear carrier 33 comprises third planetary gear shafts 44a which rotatably support the fourth planetary gears 44. The thirdplanetary gear carrier 33 is engaged with the second planetary gearcarrier 32 to transmit power from the third planetary gear carrier 33 tothe second planetary gear carrier 32.

As is readily apparent from FIG. 1, the middle axes of the secondplanetary gear shafts 42 a and the third planetary gear shafts 44 a areradially spaced apart. The middle axes of third planetary gear shafts 44a are arranged on a cylindrical plane having a larger diameter than acylindrical plane which comprises the middle axes of the secondplanetary gear shafts 42 a. The cylindrical plane which comprises themiddle axes of first planetary gear shafts 41 a corresponds to thecylindrical plane of the middle axes of third planetary gear shafts 44a. Thus, the middle axes of the second planetary gear shafts 42 a whichare arranged between the first and fourth planetary gear mechanisms 6and 9 are closer to the hub axle 1 than the middle axes of the first andthird planetary gear shafts 41 a and 44 a, respectively.

The third planetary gear carrier 33 of the fourth planetary gearmechanism 9 can be connected to the downstream planetary gear carrier31. For this purpose, the third clutch 53 mentioned above is providedbetween the third planetary gear carrier 33 and the first planetary gearcarrier 31. In particular, the third clutch 53 is arranged at an end ofthe third planetary gear carrier 33 distant from the driver 2 andengages with/disengages from the clutch engaging portion 31 c ofdownstream of the first planetary gear carrier 31. For the powertransmission from the driver 2 to the fourth planetary gear mechanism 9,fourth and fifth clutches 54 and 55 are provided.

The fourth clutch 54 is a one-way clutch disposed between the driver 2and the second ring gear 22. The second ring gear 22 comprises an axialprojection 22 a which extends towards the driver 2. The axial projection22 a comprises on its inner peripheral surface a clutch engaging portion22 b which cooperates with the fourth clutch 54 to lock or unlock thesecond ring gear 22 with the driver 2. The fourth clutch 54 is supportedby an axial projection 2 a of the driver 2 that extends in parallel withthe axial projection 22 a of the ring gear 22.

For speed stages 1 to 6, the fourth clutch 54 is engaged with the ringgear 22 to transmit power from the driver 2 to the ring gear 22.

For speed stages 7 to 11, a fifth clutch 55 is provided which isdisposed between the driver 2 and the third planetary gear carrier 33for transmitting rotational power from the driver 2 to the thirdplanetary gear driver 33. The fifth clutch 55 is formed as a clutch ringand is axially movable in a longitudinal direction of the hub axle 1.The fifth clutch 55 comprises two engaging portions 55 a, 55 b which areadapted to engage with clutch engaging portions 2 b and 33 a which areprovided on the driver 2 and the third planetary gear carrier 33,respectively.

The clutch engaging portion 2 b of the driver 2 is formed on the innerperipheral surface of the axial projection 2 a and engages with theupper or radial engaging portion 55 b of the fifth clutch 55. The clutchengaging portion 33 a of the third planetary gear carrier 33 is adaptedto engage with/disengage from the lower or axial engaging portion 55 aof the fifth clutch 55.

For speed stages 7 to 11, the axial engaging portion 55 a of the fifthclutch 55 and the clutch engaging portion 33 a of the third planetarygear carrier 33 are coupled and the fourth clutch 54 is uncoupled.

A more detailed description of the aforementioned clutch mechanismincluding the fourth and fifth clutches 54 and 55 is disclosed in EP 1323 627 A2 as well as in European Patent Application 07 001 076.4, bothowned by Shimano Inc.

The function of the hub transmission according to FIG. 1 is explainedwith reference to FIGS. 2 to 12 in which the coupling of the variouscomponents for each speed stage and the specific power transmission pathrealized thereby are illustrated. The bold lines and arrows indicated inFIGS. 2 to 12 illustrate the rotational power flow through the powertransmission mechanism 4. The coupling of the various components as wellas the power transmission paths are indicated in the following Tables 1and 2 wherein Table 1 concerns the coupling of the components and Table2 concerns the specific power transmission path.

TABLE 1 Clutch ring 55 (Driver and First Second Third Speed 3rdPlanetary Sun gear Sun gear Sun gear Stage gear carrier 33) 11 12 13Gear Ratio 1 Disengaged Free Free Free 0.527 2 Disengaged Locked FreeFree 0.681 3 Disengaged Free Free Locked 0.770 4 Disengaged Free LockedFree 0.873 5 Disengaged Locked Free Locked 0.995 6 Disengaged LockedLocked Free 1.127 7 Engaged Locked Free Free 1.292 8 Engaged Free FreeLocked 1.462 9 Engaged Free Locked Free 1.656 10 Engaged Locked FreeLocked 1.888 11 Engaged Locked Locked Free 2.139

TABLE 2 Speed Stage Power Transmission Path 1 Driver—4th clutch 54—2ndring gear 22—(4th planet gear 44 rotates around 4th sun gear 14) - 3rdplanetary gear carrier 33- 3rd clutch 53—1st planetary carrier 31—1stclutch 51—Hub Shell 2 Driver—4th clutch 54—2nd ring gear 22—(4th planetgear 44 rotates around 4th sun gear 14) - 3rd planetary gear carrier33—3rd clutch 53—1st planetary carrier 31—(1st planet gear 41 rotatesaround 1st sun gear 11)—1st ring gear 21—2nd clutch 52—Hub Shell 3Driver—4th clutch 54—2nd ring gear 22—(4th planet gear 44 rotates around4th sun gear 14)—3rd planetary gear carrier 33- 2nd planetary gearcarrier 32—(2nd planet gear 42 rotates around 2nd sun gear 12)—1stplanetary gear carrier 31—1st clutch 51—Hub Shell 4 Driver—4th clutch54—2nd ring gear 22—(4th planet gear 44 rotates around 4th sun gear14)—3rd planetary gear carrier 33—2nd planetary gear carrier 32—(2ndplanet gear 42 rotates around 2nd sun gear 12)—1st planetary gearcarrier 31—1st clutch 51 - Hub Shell 5 Driver—4th clutch 54—2nd ringgear 22—(4th planet gear 44 rotates around 4th sun gear 14)—3rdplanetary gear carrier 33—2nd planetary gear carrier 32—(3rd planet gear43 rotates around 3rd sun gear 13)—1st planetary carrier 31—(1st planetgear 41 rotates around 1st sun gear 11)—1st ring gear 21—2nd clutch52—Hub Shell 6 Driver—4th clutch 54—2nd ring gear 22—(4th planet gear 44rotates around 4th sun gear 14)—3rd planetary gear carrier 33—2ndplanetary gear carrier 32—(2nd planet gear 42 rotates around 2nd sungear 12)—1st planetary carrier 31—(1st planet gear 41 rotates around 1stsun gear 11)—1st ring gear 21—2nd clutch 52—Hub Shell 7 Driver—5thclutch 55—3rd planetary gear carrier 33—3rd clutch 53- 1st planetarycarrier 31—(1st planet gear 41 rotates around 1st sun gear 11)—1st ringgear 21—2nd clutch 52—Hub Shell 8 Driver—5th clutch 55—3rd planetarygear carrier 33—2nd planetary gear carrier 32—(3rd planet gear 43rotates around 3rd sun gear 13)—1st planetary carrier 31—1st clutch 51 -Hub Shell 9 Driver—5th clutch 55—3rd planetary gear carrier 33—2ndplanetary gear carrier 32 - (2nd planet gear 42 rotates around 2nd sungear 12)—1st planetary gear carrier 31 - 1st clutch 51—Hub Shell 10Driver—5th clutch 55—3rd planetary gear carrier 33—2nd planetary gearcarrier 32—(3rd planet gear 43 rotates around 3rd sun gear 13)—1stplanetary gear carrier 31—(1st planet gear 41 rotates around 1st sungear 11)—1st ring gear 21—2nd clutch 52—Hub Shell 11 Driver—5th clutch55—3rd planetary gear carrier 33—2nd planetary gear carrier 32—(2ndplanet gear 42 rotates around 2nd sun gear 12)—1st planetary gearcarrier 31—(1st planet gear 41 rotates around 1st sun gear 11)—1st ringgear 21—2nd clutch 52—Hub Shell

In summary, the hub transmission according to the described embodimentof the invention allows the realization of an 11 speed internal hubtransmission wherein the diameter of the hub shell 2 is similar to thediameter of a currently available 8 speed hub transmission. This meansthat the hub transmission of the invention provides more speed stagesthan the conventional hub transmission without increasing the hubdiameter. Moreover, the hub transmission according to FIG. 1 providesthe advantage that all transmission paths are simple which leads to anefficient power transmission.

In general, the planetary gear carrier 31 of the downstream planetarygear unit 6 has an axially elongated shape adapted to mesh with theplanetary gears 43 of the upstream planetary gear mechanism 8. Theaxially elongated shape of the downstream planetary gear carrier 31allows for a compact, small diameter internal hub transmission for abicycle with highly efficient transmission paths. Moreover, the axiallyelongated shape of the planetary gear carrier 31 allows for coupling anduncoupling the planetary gear carrier 31 with/from a planetary gearcarrier 33 of a further upstream planetary gear mechanism 9. Inparticular, the axially elongated planetary gear carrier 31 of thedownstream planetary gear unit 6 is adapted to selectively transmitrotational power from the planetary gears 43 of the upstream planetarygear mechanism 8 and to selectively transmit rotational power from theplanetary gear carrier 33 of the further upstream planetary gearmechanism 9.

FIGS. 1 to 12 refer to a hub transmission without a brake unit toexplain the design and function of the gear mechanisms provided in thehub transmission. The hub transmission according to FIGS. 1 and 12 issupplemented in FIGS. 13 to 17 by a brake unit 80 which is coupled withthe most downstream planetary gear unit to produce a braking force ifthe planetary gear mechanism is rotated in a reverse direction. Theplanetary gear mechanisms shown in FIGS. 1 to 12 and explained in thefollowing in detail correspond to the planetary gear mechanisms of thehub transmissions according to FIGS. 13 to 17. In other words,embodiments of the hub transmission with a coaster brake are illustratedin FIGS. 13 to 17 with the gear mechanism of the hub transmissions beingsubstantially the same as in FIGS. 1 to 12. The hub transmissionaccording to FIGS. 1 to 12 is modified in FIGS. 13 to 17 insofar asclutches 53 a and 54 b are used that allow transmitting a reverserotational force from driver 2 to the brake unit 80 which is coupledwith the gear mechanism. The brake unit 80 is explained with referenceto FIGS. 13 and 15. The same brake unit 80 is also used in theembodiment according to FIG. 14.

The brake unit 80 is disposed distant from the driver 2 and isoperatively connected with the driver 2 by the planetary gear mechanismsarranged therebetween. The brake unit 80 includes a cup 81 which isnon-rotatably connected with the hub shell 3, and therefore allows thetransmission of a rotational force to the hub shell 3. The cup 81 formsa circumferentially disposed braking surface 82 against which aplurality of brake elements 83 can be pressed to transmit a reversebraking torque to the hub shell 3.

The brake elements 83 are preferably formed by a plurality ofcircumferentially disposed arcuate brake shoes which are biased radiallyinwardly from the braking surface 82 by means of a brake spring 86. Thisarrangement is shown in FIG. 13. FIG. 15 schematically shows the brakeelement 83 as one ring. The brake elements 82 are actuated by means of aplurality of control elements 84 in the form of rollers which aredisposed circumferentially on an axial end 31 g of the planetary gearcarrier 31 of the downstream planetary gear unit 6. The axial end 31 gof the planetary gear carrier 31 comprises on its outer peripheralsurface cam portions or cam surfaces 31 f which cooperate with theplurality of rollers or control elements 84 to move same in a radiallyoutward direction for actuating brake elements 83 if the planetary gearcarrier 31 rotates in a reverse direction.

The control elements 84 or the rollers, respectively, are held by aretaining element 85 which is designed as a roller cage supporting theplurality of circumferentially disposed rollers. The retaining element85 is engaged with the planetary gear carrier 31 of the downstreamplanetary gear mechanism 6. The retaining element 85 comprises aradially extending projection 85 a which is disposed between the brakeunit 80 and the first planetary gear carrier 31 of the downstreamplanetary gear mechanism 6. A projection 85 a of the retaining element85 forms a circumferential support surface 85 b.

On the support surface 85 b, the first clutch 51 is provided whichcouples the retaining element 85 and the cup 81. The clutch 51 includesa plurality of circumferentially supposed pawls which are mounted to theretaining element 85 and the roller cage, respectively, and are biasedradially outwardly by pawl springs for engaging an inner peripheral gear81 a formed on an inner side of cup 81. The pawls of the clutch 51transmit a forward rotation of the first planetary gear carrier 31 tothe cup 81 and hence to the hub shell 3.

To effect the reverse rotation of the planetary gear mechanisms 6, 7, 8and 9 in order to apply a braking torque to the hub shell 3, third andfourth one-way clutches 53 and 54 according to FIGS. 1 to 12 arereplaced in the embodiment according to FIG. 13 by third and fourthtwo-way clutches 53 b and 54 b. Also, two-way clutches 53 a and 54 a aredesigned to transmit both a forward driving torque and a reverse brakingtorque. The design of the clutches 53 a and 54 a corresponds to thedesign disclosed in EP Patent Publication No. 1 413 509 B1 which isassigned to Shimano, Inc. In particular, the fourth clutch 54 a includesa plurality of circumferentially disposed pawls 54 b which engage withan inner peripheral gear portion of the second ring gear 22, inparticular the clutch engaging portion 22 b. The pawls 54 b are biasedradially outwardly by a pawl spring, and thus, function as a one-wayclutch between the driver 2 and the second ring gear 22. A plurality of(braking) pawls 54 c is circumferentially disposed for driving thesecond ring gear 22 in a rearward direction. The third clutch 53 a isdesigned correspondingly to fourth clutch 54 a.

The embodiment according to FIG. 13 functions as follows.

The driver 2 rotates relative to the second ring gear 22 with smallangles as play. The pawls 54 b and 54 c are supported by a pawl controlcage and a ring spring disposed between the driver 2 and the second ringgear 22. When the driver 2 rotates in a reverse direction, a relativerotation between the driver 2 and the second ring gear 22 occurs atsmall angles and, at the same time, the ring spring rotates with thedriver 2 in a reverse direction. The reverse rotation of the ring springcauses a reverse rotation of pawl control cage which, in turn, providesfor bringing down the driving pawls 54 b and bringing up the brakingpawls 54 c. Since the braking pawls 54 c engage with the inner teeth ofthe clutch engaging portion 22 b of the second ring gear 22, a reverserotational force of the driver 2 is transmitted to the second ring gear22 via the braking pawls 54 c. Accordingly the second ring gear 22rotates in a reverse direction.

As fourth sun gear 14 meshes with the fourth planetary gear 44, thereverse rotational force of the second ring gear 22 is transmitted tothird planetary gear carrier 33.

As pawl control cage and ring spring of third clutch 53 a disposedbetween the third carrier 33 and the first planetary gear carrier 31,the pawl control cage and the ring spring of third clutch 53 a rotate ina reverse direction with the third carrier 33 within play. The pawlcontrol cage of the third clutch 53 a causes the driving pawls 53 b todisengage and to engage the braking pawls 53 c with the first planetarygear carrier 31. Accordingly, the first planetary gear carrier 31rotates in a reverse direction.

Thus, the control elements 84 are outwardly forced by means of the camsurfaces 31 f thereby applying a braking torque to the cup 81 and,hence, to the hub shell 3.

The further embodiment according to FIG. 14 corresponds to theembodiment according to FIG. 13 except for the third clutch 53 a whichis replaced with an arrangement comprising a linking member 70 and a oneway clutch 53.

The function of the linking member 70 is to control the driving pawls ofthe third clutch 53, to control the braking pawls 53 c between thelinking member 70 and the third planetary gear carrier 33 and totransmit a braking rotation (reverse rotation) from the third planetarygear carrier 33 to the first planetary gear carrier 31. Thus, thelinking member 70 controls to bring up or bring down the driving pawlsand the braking pawls which are responsible for the forward or reverserotation of the first planetary gear carrier 31. The linking member 70has the form of a ring gear which meshes with the planetary gears 43 ofthe third planetary gear mechanism 8 without play and connects with thefirst planetary gear carrier 31 with play. Thus, the linking member 70and the first planetary gear carrier 31 can rotate relative to eachother within the predetermined play. A more detailed description of thelinking member 70 is contained in EP Patent Publication No. 06 008 957which is assigned to Shimano, Inc.

The embodiment according to FIG. 14 functions as follows:

If the driver 2 rotates in a reverse or backward direction, the thirdplanetary gear carrier 33 also rotates in a backward direction. Then,the linking member 70 rotates relative to the first planetary gearcarrier 31 within the play in a reverse direction. Then, the drivingpawls 53 will take the inner teeth of the first planetary gear carrier31 with the result that a reverse rotational force is transmitted fromthe third planetary gear carrier 33 to the first planetary gear carrier31 via the braking pawls 53 c of the third clutch 53. Therefore, in allspeed stages, the transmission path of the reverse rotation force is thesame path with the result that the brake power (torque) is alwaysconstant.

As regards the forward rotation the hub transmission is in a drivingstage, it should be noted that, if the driver 2 rotates in a forwarddirection, the third planetary gear carrier 33 also rotates in a forwarddirection. In the first, the second and the seventh speed stage, theforward rotational force is transmitted from the third planetary gearcarrier 33 to the first planetary gear carrier 31 via the driving pawls53 b of the third clutch 53. Thus, the first planetary gear carrier 31rotates with the same speed as the linking member 70 in a forwarddirection.

In the other speed stages, the forward rotational force is transmittedfrom the third planetary gear carrier 33 to the first planetary gearcarrier 31 via the second or the third planetary gear mechanisms 7, 8and the linking member 70. In these speed stages, the first planetarygear carrier 31 rotates faster than the linking member 70 in a forwarddirection. In this case, the linking member 70 rotates relatively to theplanetary gear carrier 31 within the play in the forward direction.

The braking torque path in the embodiment according to FIG. 13 isindicated by the arrow in FIG. 16 and comprises the following elements:the driver 2—the braking pawl 54 c of the fourth clutch 54 a—the secondring gear 22—(the fourth planetary gears 44 rotate around the fourth sungear 14)—the third planetary gear carrier 33—the braking pawls 53 c ofthe third clutch 53 a—the first planetary gear carrier 31—the controlelements (brake rollers) 84—the braking element (brake shoe) 83—thebraking surface 82—the cup 81—the hub shell 3.

The braking path (reverse rotation path) of the embodiment according toFIG. 14 comprises the following elements: the driver 2—the braking pawl54 c of the fourth clutch 54 a—the second ring gear 22—(the fourthplanetary gears 44 rotate around the fourth sun gear 14)—the thirdplanetary gear carrier 33—the braking pawls 53 c of the third clutch53—the linking member 70—the first planetary gear carrier 31 the controlelements (brake rollers) 84—the braking elements (brake shoes) 83—thebraking surface 82—the cup 81—the hub shell 3.

GENERAL INTERPRETATION OF TERMS

In understanding the scope of the present invention, the term“comprising” and its derivatives, as used herein, are intended to beopen ended terms that specify the presence of the stated features,elements, components, groups, integers, and/or steps, but do not excludethe presence of other unstated features, elements, components, groups,integers and/or steps. The foregoing also applies to words havingsimilar meanings such as the terms, “including”, “having” and theirderivatives. Also, the terms “part,” “section,” “portion,” “member” or“element” when used in the singular can have the dual meaning of asingle part or a plurality of parts.

While only selected embodiments have been chosen to illustrate thepresent invention, it will be apparent to those skilled in the art fromthis disclosure that various changes and modifications can be madeherein without departing from the scope of the invention as defined inthe appended claims. For example, the size, shape, location ororientation of the various components can be changed as needed and/ordesired. Components that are shown directly connected or contacting eachother can have intermediate structures disposed between them. Thefunctions of one element can be performed by two, and vice versa. Thestructures and functions of one embodiment can be adopted in anotherembodiment. It is not necessary for all advantages to be present in aparticular embodiment at the same time. Every feature which is uniquefrom the prior art, alone or in combination with other features, alsoshould be considered a separate description of further inventions by theapplicant, including the structural and/or functional concepts embodiedby such feature(s). Thus, the foregoing descriptions of the embodimentsaccording to the present invention are provided for illustration only,and not for the purpose of limiting the invention as defined by theappended claims and their equivalents.

1. A bicycle hub transmission comprising: a hub axle; a driver rotatablysupported relative to the hub axle; a hub shell rotatably supportedrelative to the driver, a power transmission mechanism including adownstream planetary gear unit and an upstream planetary gear unit,which are operatively disposed between the driver and the hub shell toselectively transmit rotational power from the driver to the hub shellthrough one a plurality of power transmission paths; and a shiftmechanism operatively coupled to the power transmission mechanism toselecting one of the power transmission paths, the downstream planetarygear unit including a planetary gear carrier that meshes with planetarygears of the upstream planetary gear unit or with a linking member whichis coupled to the planetary gears of the upstream planetary gear unit,and the planetary gear carrier of the downstream planetary gear unitbeing coupled with a brake unit disposed within the hub shell totransmit a reverse rotational power from the driver to the brake unit,the planetary gear carrier of the downstream planetary gear unitincludes a carrier portion and a ring gear portion which meshes with theplanetary gears of the upstream planetary gear unit or with the linkingmember, which is coupled with the planetary gears of the upstreamplanetary gear mechanism, with the carrier portion and the ring gearportion being non-rotatably connected as a unit.
 2. The bicycle hubtransmission according to claim 1, wherein the downstream planetary gearunit and the upstream planetary gear unit form at least four planetarygear mechanisms arranged in series.
 3. The bicycle hub transmissionaccording to claim 1, wherein the upstream planetary gear unitconstitutes at least second, third and fourth planetary gear mechanisms.4. The bicycle hub transmission according to claim 3, wherein thedownstream planetary gear unit and the third gear mechanism include theplanetary gears of the upstream planetary gear unit.
 5. The bicycle hubtransmission according to claim 3, wherein the planetary gear carrier ofthe downstream planetary gear unit is selectively connectable with thefourth planetary gear mechanism.
 6. The bicycle hub transmissionaccording to claim 5, wherein the planetary gear carrier of thedownstream planetary gear unit includes a clutch engaging portion whichis selectively connectable with a planetary gear carrier of the fourthplanetary gear mechanism.
 7. The bicycle hub transmission according toclaim 1, wherein the planetary gear carrier of the downstream planetarygear unit is selectively connectable with the hub shell by a firstclutch to transmit a rotational force from the planetary gear carrier tothe hub shell.
 8. The bicycle hub transmission according to claim 7,wherein the brake unit includes a cup which is non-rotatably connectedwith the hub shell and forms a circumferentially disposed brakingsurface, a plurality of brake elements arranged to co-operate with thebraking surface to apply a braking torque, and a plurality of controlelements to actuate the brake elements, with the control elements beingcoupled with the planetary gear carrier of the downstream planetary gearunit such that an actuation of the brake elements is effected by areverse rotation of the planetary gear carrier of the downstreamplanetary gear unit.
 9. The bicycle hub transmission according to claim8, wherein the first clutch is disposed between the cup and theplanetary gear carrier of the downstream planetary gear unit.
 10. Thebicycle hub transmission according to claim 8, wherein the first clutchis supported by a retaining element of the control elements.
 11. Thebicycle hub transmission according to claim 10, wherein the controlelements includes a plurality of rollers which co-operate with aplurality of cam surfaces provided on the planetary gear carrier of thedownstream planetary gear unit, and the retaining element includes aroller cage supporting the rollers with the roller cage being engagedwith the planetary gear carrier of the downstream planetary gear unit.12. A bicycle hub transmission comprising: a hub axle; a driverrotatably supported relative to the hub axle; a hub shell rotatablysupported relative to the driver; a power transmission mechanismincluding a downstream planetary gear unit and an upstream planetarygear unit, which are operatively disposed between the driver and the hubshell to selectively transmit rotational power from the driver to thehub shell through one a plurality of power transmission paths; and ashift mechanism operatively coupled to the power transmission mechanismto selecting one of the power transmission paths, the downstreamplanetary gear unit including a planetary gear carrier that meshes withplanetary gears of the upstream planetary gear unit or with a linkingmember which is coupled to the planetary gears of the upstream planetarygear unit, and the planetary gear carrier of the downstream planetarygear unit being coupled with a brake unit to transmit a reverserotational power from the driver to the brake unit, the downstreamplanetary gear unit constituting at least a first planetary gearmechanism including a first sun gear, a first ring gear and a pluralityof first planetary gears, with the first sun gear being rotatablysupported by the hub axle and selectively lockable with the hub axle,the first ring gear being coaxially arranged with the first sun gear,and the first planetary gears meshing with the first sun gear and thefirst ring gear, the first planetary gears being rotatably supported bythe planetary gear carrier of the first planetary gear mechanism, thefirst ring gear being selectively connectable with the hub shell by asecond clutch for transmitting a rotational force from the first ringgear to the hub shell, the upstream planetary gear unit constituting atleast second, third and fourth planetary gear mechanisms, the secondplanetary gear mechanism includes a second sun gear, a second planetarygear carrier and a plurality of second planetary gears, with the secondsun gear being rotatably supported by the hub axle and selectivelylockable with the hub axle, the second planetary gear carrier beingrotatably supported by the second planetary gear carrier and meshingwith the second sun gear.
 13. The bicycle hub transmission according toclaim 12, wherein the third planetary gear mechanism includes a thirdsun gear rotatably supported by the hub axle and selectively lockablewith the hub axle, with the planetary gears being rotatably supported bythe second planetary gear carrier and meshed with the third sun gear.14. The bicycle hub transmission according to claim 13, wherein theplanetary gear carrier of the third planetary gear mechanism and thesecond planetary gears of the second planetary gear mechanism arenon-rotatably connected as a unit to form stepped planetary gearsrespectively.
 15. The bicycle hub transmission according to claim 14,wherein the fourth planetary gear mechanism includes a fourth sun gear,a second ring gear and a plurality of fourth planetary gears, with thefourth sun gear being non-rotatably fixed to the hub axle, the secondring gear being coaxially arranged with the fourth sun gear, and thefourth planetary gears being rotatably supported by a third planetarygear carrier and meshing with the fourth sun gear and the second ringgear.
 16. The bicycle hub transmission according to claim 15, whereinthe third planetary gear carrier engages with the second planetary gearcarrier.
 17. The bicycle hub transmission according to claim 15, furthercomprising a third clutch is disposed between the third planetary gearcarrier and the first planetary gear carrier, with clutch engagingportion arranged to selectively transmit a rotational force from thethird planetary gear carrier to the first planetary gear carrier. 18.The bicycle hub transmission according to claim 17, further comprising afourth clutch is disposed between the driver and the second ring gear toselectively transmit a rotational force from the driver to the secondring gear.
 19. The bicycle hub transmission according to claim 18,further comprising a fifth clutch is disposed between the driver and thethird planetary gear carrier to selectively transmit a rotational forcefrom the driver to the third planetary gear carrier.
 20. The bicycle hubtransmission according to claim 18, wherein the fourth clutch includes aplurality of driving pawls and a plurality of braking pawls which arearranged to be selectively activated by a forward or reverse rotation ofthe driver to rotate the second ring gear in a forward or reversedirection.
 21. The bicycle hub transmission according to claim 17,wherein the third clutch includes a plurality of driving pawls and aplurality of braking pawls which are arranged to be selectivelyactivated by a forward or reverse rotation of the third planetary gearcarrier to rotate the first planetary gear carrier in a forward orreverse direction.
 22. The bicycle hub transmission according to claim17, wherein the third clutch includes a plurality of driving pawls, andthe linking member includes a plurality of braking pawls, with the thirdclutch and the linking member being coupled such that the driving pawlsof the third clutch are disengaged and the braking pawls of the linkingmember are engaged by a reverse rotation of the third planetary gearcarrier.